The disc brake is a lot like the brakes on a
bicycle. Bicycle brakes
have a caliper, which squeezes the brake pads against the wheel. In a disc
brake, the brake pads squeeze the rotor instead of the wheel, and the
force is transmitted
hydraulically instead of through a cable.
Friction between the pads
and the disc slows the disc down.

A moving car has a certain amount of kinetic energy, and the brakes have to
remove this energy from the car in order to stop it. How do the brakes do this?
Each time you stop your car, your brakes convert the kinetic energy to heat
generated by the friction between the pads and the disc. Most car disc brakes
are vented.

Vented disc brakes have a set of vanes, between the
two sides of the disc, that pumps air through the disc to provide cooling.

Self-Adjusting
Brakes
The single-piston floating-caliper disc brake is self-centering and
self-adjusting. The caliper is able to slide from side to side so it will
move to the center each time the brakes are applied. Also, since there is no
spring to pull the pads away from the disc, the pads always stay in light
contact with the rotor (the rubber piston seal and any wobble in the rotor may
actually pull the pads a small distance away from the rotor). This is important
because the pistons in the brakes are much larger in diameter than the ones in
the master cylinder. If the brake pistons retracted into
their cylinders, it might take several applications of the brake pedal to pump
enough fluid into the brake cylinder to engage the brake pads. Older cars had
dual or four-piston fixed-caliper designs. A piston (or two) on each side of the
rotor pushed the pad on that side. This design has been largely eliminated
because single-piston designs are cheaper and more reliable.

Servicing Your
Brakes
The most common type of service required for brakes is changing the pads.
Disc brake pads usually have a piece of metal on them called a wear indicator.

When enough of the friction material is worn away, the wear indicator will
contact the disc and make a squealing sound. This means it is time for new brake
pads.